A Tennessee bill meant to protect teachers who allow students to question and criticize "controversial" subjects such as evolution and climate change became law on Tuesday after Gov. Bill Haslam (R) declined to act.

The state legislature had sent the bill to Haslam earlier this month. He had until Tuesday to veto it, sign it or allow it to pass without his signature.

Critics of the legislation have dubbed it the "Monkey Bill" and charge that it is anti-science, backdoor approval of the teaching of religion in schools that reminds of the state's history with the Scopes Trial.

"It would open the door to creationism, it would open the door to climate change denial, and to other sorts of pseudosciences being introduced into Tennessee classrooms," Josh Rosenau of the National Center for Science Education told The Huffington Post last month.

Haslam claimed to have looked into the potential effects of the legislation and had determined that opponents' worries about the broader impacts on the state's public school curriculum were unwarranted. But on Tuesday, Haslam expressed "concern" about potential "confusion" stemming from the measure in a statement regarding his inaction:

I have reviewed the final language of HB 368/SB 893 and assessed the legislation's impact. I have also evaluated the concerns that have been raised by the bill. I do not believe that this legislation changes the scientific standards that are taught in our schools or the curriculum that is used by our teachers. However, I also don’t believe that it accomplishes anything that isn’t already acceptable in our schools.

The bill received strong bipartisan support, passing the House and Senate by a three-to-one margin, but good legislation should bring clarity and not confusion. My concern is that this bill has not met this objective. For that reason, I will not sign the bill but will allow it to become law without my signature.

It's the first bill Haslam has allowed to become law without his signature.